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Full text of "Geologic investigation of roof and floor strata : Longwall demonstration, Old Ben Mine no. 24 : final technical report, no. 1"

557.09773 
I IL6cr 1982-2 

ISGS CONTRACT/GRANT REPORT: 1982-2 



U.S. D.O.E. ET-76-G-01-9007 



Geologic Investigation 
of Roof and Floor Strata: 
Longwall Demonstration, 
Old Ben Mine No. 24 



Robert A. Bauer 
Philip J. DeMaris 



April 1982 

Illinois Department of Energy and Natural Resources 
STATE GEOLOGICAL SURVEY DIVISION 
Champaign, Illinois 



Bauer, Robert A. 

Geologic investigation of roof and floor strata: longwall 
demonstration, Old Ben Mine No. 24, final technical report: 
part 1 / Robert A. Bauer and Philip J. DeMaris. - Champaign, 
III. : Illinois State Geological Survey, April 1982. 

49 p. ; 29 cm. - (Illinois-Geological Survey. Contract/Grant 
report ; 1982-2) (DOE/ET/12177-1) (FE/9007-1) 

Also published by U.S. Department of Energy, Division of 
Fossil Fuel Extraction. 

1. Coal mines and mining. 2. Coal balls. 3. Mine roofs (stability). 
I. DeMaris, Philip J. II. Title. III. Series 1. IV. Series 2. V. Series 3. 



Printed by authority of the State of Illinois/ 1982/250 



ISGS CONTRACT/GRANT REPORT 1982-2 FE/9007-1 

DOE/ET/12177-1 



GEOLOGIC INVESTIGATION OF ROOF AND FLOOR STRATA: 
LONGWALL DEMONSTRATION, OLD BEN MINE NO. 24 



FINAL TECHNICAL REPORT: PART 

by 

Robert A. Bauer and Philip J. DeMaris 

Principal Investigators: 

Heinz H. Damberger 

Harold J. Gluskoter (to 6/78) 



April 1982 

Contract No. U.S.D.O.E. ET-76-G-01-9007 
(Formerly U.S.B.M. G0166207) 

This report represents work on a program 

that was originated by the Interior Department's Bureau of Mines 

and was transferred to the Department of Energy on October 1, 1977. 



Illinois State Geological Survey 
Natural Resources Building 
615 East Peabody Drive 
Champaign, I L 61820 



Digitized by the Internet Archive 

in 2012 with funding from 

University of Illinois Urbana-Champaign 



http://archive.org/details/geologicinvestig19822baue 



CONTENTS 

Abstract v 

Acknowledgments v 

Introduction 1 

Geology of Herrin (No. 6) Coal in Franklin County 2 

Geologic Characteristics of Old Ben No. 24 Mine Area 

Setting 6 

Roof 9 

Coal 14 

Floor 14 

Rolls 18 

Coal balls 21 
Mining Problems 25 

Prediction of coal balls 25 

Roof stability 27 

Subsidence 34 

Physical strength results 35 
Further Research Directions 37 
References 38 
Appendix A. Testing Procedures 41 

Unconfined strength and elastic modulus 41 

Indirect tensile strength 41 

Water content 41 

Specific gravity 42 

Shore hardness 42 

Slake durability 42 
Appendix B. Core Descriptions and Test Results 43 

ISGS Drill Hole LW-1 43 

ISGS Drill Hole LW-2 46 

ISGS Drill Hole LW-3 48 



TABLES 

1. Identified plant material by plant group 

from coal ball vertical section 3 in Area L 21 

2. Occurrence of fallen intersections for mapped area B 
by categories of roof lithology and structure 34 

3. Number of mapped falls by location for mapped area B 34 



FIGURES 

1. Distribution of the Herrin (No. 6) Coal Member in southern Illinois 
and the location of the study area, Franklin County 3 

2. Composite stratigraphic section of the roof of the longwall panels 4 

3. Thickness of the interval between the top of the Springfield (No. 5) Coal 
and the base of the Herrin (No. 6) Coal in Franklin County 5 

4. Generalized thickness of Herrin (No. 6) Coal in Franklin County 5 

5. Distribution and thickness of the Energy Shale Member in a portion of Franklin County 7 

6. Index to mapped areas in the Old Ben Coal Company Mine No. 24 8 

7. Plan view of roof geology at the longwall demonstration site in mapped area A 10 

8. Schematic cross section showing interrelationships of Herrin Coal, rolls, and immediate roof members 

9. Spatial relationship of mapped areas A and B and the sinuous exposure of Anna Shale roof 12 
10. Map of the roof geology for mapped area B 13 

11a. Clay mineral compositions of the Energy Shale and roll material 15 

11b. Clay mineral analyses of the Anna Shale showing differences 

of clay mineral content between the upper and lower portions of the unit 15 

12. Coal thickness variation by roof lithology 16 

13. Correlation of macropetrographic units with the Herrin (No. 6) Coal along a 1,000-foot traverse 17 

14. Clay mineral composition of underclay samples 18 

15. Idealized cross sections of rolls showing variation in fill materials 20 

16. Concentrated coal balls near the center of coal-ball area L 23 

17. Map of area M showing limits of the "core" of concentrated coal balls 23 

18. Coal balls, coal-ball areas, and roof lithologies identified during mapping of the 3 longwall panels 24 
19a. Five of the 13 positions where coal and coal balls were measured separately 26 

19b. Small compaction fault under round coal ball has displaced thin coal ball about 1 cm. 26 

20. Plan view (above) and cross section of roof fall in relation to mine and geologic setting 29 

21. Slips in roof shown paralleling black shale roof exposure (area B) 30 

22. Roof fall in relation to mine plan and geologic setting 31 

23. North-south fractured zone in roof caused by large horizontal compressive forces 32 

24. Roof falls in the Energy Shale showing a preferential north-south orientation 33 
25a. Subsidence profile above the second longwall panel 36 

25b. Subsidence profile above the first longwall panel 36 



ABSTRACT 

In-mine mapping of three longwall panels at the Old Ben No. 24 Mine has revealed 
both major and minor roof -stability problems and multiple areas of concentrated coal balls 
within the Herrin (No. 6) Coal Member. The roof-stability problems are related to three 
interacting factors: variations in roof lithology, various structural features, and mining plan. 
Major roof-stability problems are rare at the longwall face, but more common in the 
longwall support entries. Several major falls have occurred in areas where potential problems 
were identified previously during mapping. Lesser roof-stability problems are associated 
with "rolls" (linear shale bodies in the top of the seam) containing compaction faults 
and with a tectonic fault zone running perpendicular to the face of the second panel. 

A distinctive roof type has been identified in this mine; the roof type varies between 
Energy Shale and Anna Shale /Brereton Limestone over a short distance. Other mines 
with this type of transitional roof can expect similar roof problems. 

Large deposits of coal balls within the seam repeatedly interfere with orderly development 
of support entries and damage longwall equipment. The second and third panels have 
been shortened to avoid areas of coal-ball concentrations. The distribution of coal balls 
is strongly correlated with roof lithology; thus the association of roof and coal balls 
has been used successfully to predict locations of coal balls in unmined areas. 



ACKNOWLEDGMENTS 

This report is based on detailed geologic investigations in the Old Ben 
No. 24 Mine near Benton, Illinois, in conjunction with the longwall coal 
mining demonstration project. This work was supported by the U.S. Bu- 
reau of Mines Grant G0166207 from September 1976 to March 1978, and by 
the Department of Energy Grant ET-76-G-01-9007 from April 1978 to Decem- 
ber 1979. The work was administered under the technical direction of the 
Pittsburgh Mining Technology Center with James R. White, and later, Mary 
Ann Gross as Technical Project Officers. 

We wish to thank the officials and employees of the Old Ben Coal Company 
and of their No. 24 Mine for valuable information and assistance. We 
also wish to thank W. John Nelson and John T. Popp of the Illinois State 
Geological Survey for assistance in underground mapping and Peter R. 
Johnson for petrographic study of the Herrin (No. 6) Coal seam in the 
study area. We are grateful to Tom Phillips of the University of Illi- 
nois, Botany Department, for identification of the plant material in the 
coal balls found in the mine. We also thank Sue M. Rimmer for clay 
mineral analyses of roof, floor, and in-seam materials. 



INTRODUCTION 

In the 1960s and early 1970s, ten attempts at longwall mining were 
made in southern Illinois in the Herri n (No. 6) Coal Member. All 
attempts were abandoned before the completion of one entire panel. The 
most serious problems were related to the chock supports, which were 
inadequate to hold the roof at the face. Since geologic conditions 
encountered during these first attempts were not documented, how geologic 
conditions related to the stability problems is not entirely known. 
Moroni (1974) described several of the longwall attempts of the Old Ben 
Coal Company; Harrell (1974) described similar attempts by Freeman Coal 
Mining Company. 

In 1975, the U.S. Bureau of Mines and the Old Ben Coal Company began a 
longwall demonstration project on a cost-sharing basis. The Illinois 
State Geological Survey, with financial support from the U.S. Bureau of 
Mines and later the U.S. Department of Energy, documented the geologic 
conditions encountered during the longwall mining demonstration. 

This report summarizes the observations made by Illinois State Geological 
Survey staff during geological mapping, sample collection, and testing 
conducted in connection with the three longwall demonstration panels and 
other selected areas in the Old Ben Coal Company No. 24 Mine. It also 
contains information from past State Geological Survey investigations 
and drill hole logs. Our tasks and goals were 

1. to map lithologic variations and geologic structures in 
roof, floor, and coal in and around the longwall panels 
and other locations in the mine (methodology generally 
follows that discussed in Krausse et al . , 1979a; 1979b); 

2. to relate geological features to the stability of the roof 
during the longwall mining operation; 

3. to drill several boreholes into the roof and floor and 
conduct mechanical strength tests on the cores; 

4. to study the nature and occurrence of coal balls found in 
the coal seam in the demonstration area for the purpose of 
predicting other coal -ball occurrences. 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



GEOLOGY OF HERRIN (NO. 6) COAL MEMBER 
AND ASSOCIATED STRATA IN FRANKLIN COUNTY 

This longwall demonstration project was conducted in the Illinois Basin 
Coal Field at the Old Ben No. 24 Mine, which is located in southern Illi 
nois within Franklin County and operates in the Herri n (No. 6) Coal Mem- 
ber (fig. 1) of the Carbondale Formation of the Pennsylvanian System 
(fig. 2 



J: 



A large river was contemporaneous with the deposition of the peat that is 
now the Herrin (No. 6) Coal. The position of the river is now repre- 
sented by the sediment-filled Walshville channel, located about 7 miles 
west of the longwall site. Shale splits within the coal seam along the 
channel indicate that the river associated with the Walshville channel 
remained active throughout deposition of the Herrin peat (Johnson, 1972). 
Furthermore, an investigation of the thickness and type of strata below 
the Herrin (No. 6) Coal showed that the river responsible for the Walsh- 
ville channel was active even before deposition of coal -forming peat 
began in Franklin County. The thickness of the interval between the 
Herrin (No. 6) Coal and the next major coal seam below, the Springfield 
(No. 5) Coal Member, varies greatly in the county. The interval is thin- 
nest near to and thickens away from the channel. The thickness of the 
interval was used as an indicator of the relative topography upon which 
the peat forming the Herrin (No. 6) Coal was deposited. Whereas the 
Herrin peat may have been slightly time transgressive, the effect within 
the study area was judged to be insignificant. Further investigation of 
strata below the Springfield (No. 5) Coal showed that no variations in 
thickness existed that might have influenced these upper units. 
In western Franklin County the interval between the Herrin (No. 6) and 
the Springfield (No. 5) Coals thins abruptly within a mile-wide, crescent- 
shaped depression that has both ends terminating near the Walshville 
channel; it appears to be an abandoned meander (fig. 3). The coal is 
thickest in the meander (fig. 4). Shape, location, and increased coal 
thickness all indicate that the meander was formed and abandoned before 
peat deposition began. 

After deposition of peat ceased, the river persisted a while, forming the 
first layer on top of the coal— a gray silty shale called the Energy 
Shale Member. This shale, believed to be an overbank deposit of the river, 
is found in several large lobate deposits along the former course of the 
river; they all thin away from the channel. The next layer deposited on 
the gray shale, or directly on the coal where the gray shale is missing, 
is a black carbonaceous shale known as the Anna Shale Member. The Anna 
Shale here is a widespread, black, highly carbonaceous shale averaging 
2.8 feet thick with a low-diversity marine fauna suggestive of a restricted 
environment. Where the Energy Shale exceeds about 35 to 45 feet in thick- 
ness, the Anna Shale generally pinches out. 

2 ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



Walshville channel; coal missing 
Energy Shale associated 
with the Walshville channel 
iil&j Clastic deposits associated with 
the New Goshen channels 
* Low-sulfur coal reported (< 2.5% S; each 
point generally represents several analyses) 
-x"^* Limit of Herrin (No. 6) Coal 
N New Goshen channels 




Franklin Co. 



Figure 1. 



Distribution of the Herrin (No. 6) Coal Member in southern Illinois, and the location of the study 
Franklin County. (From Treworgy and Jacobson, in press.) 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



I V Named Members 

r . 1 . 11 



h-6 

4 
-2 
-0 



Figure 2. 



TTTTT 



5& 



1 , 1 , 1 



15=° 



r~n 



Bankston Fork Limestone 



Lawson Shale 



Conant Limestone 
Jamestown Coal 



Figure 3 

Thickness of the interval 
between the top of the 
Springfield (No. 5) Coal 
and the the base of the 
Herrin (No. 6) Coal in 
Franklin County. 



Brereton Limestone (4 to 5 ft) 
Anna Shale (2.8 to 3.7 ft) 

Energy Shale (0 to 18 ft) 
Herrin (No. 6) Coal (Top) 



Figure 4 

Generalized thickness 
(in feet) of Herrin 
(No. 6) Coal in 
Franklin County. 



Composite stratigraphic section of the roof of the longwall panels, representing 
a portion of the Carbondale Formation, Kewanee Group, Pennsylvanian System. 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 





INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



The Breretcn Limestone Member is the next younger unit. Here the Brereton 
Limestone is dark gray, fine grained, and argillaceous. It contains an 
open-marine fauna, averages 5.9 feet thick near the mine, and overlies 
the Anna Shale or the coal, if both the Energy Shale and the Anna Shale 
are absent. Where the Energy Shale is thicker than 35 to 45 feet, the 
Brereton Limestone also pinches out. 

Each of these units may form the immediate roof within a small area; 
therefore, this type of roof is considered transitional between the 
thick Energy Shale roof found locally near the Walshville channel, and 
the Anna Shale/Brereton Limestone roof found well away from the channel. 
This variability was first recognized during in-mine mapping in Old Ben 
No. 24 (DeMaris and Bauer, 1978), and was defined as that area where the 
roof varied from Energy Shale to Anna Shale/Brereton Limestone and back 
to Energy Shale over a short distance. On the basis of further in-mine 
mapping and analysis of nearby drill-hole data we now recognize that 
Energy Shale was originally deposited over the Herrin (No. 6) and then 
partially or completely eroded. The term "transitional roof" has since 
been extended to include areas with similar variability, which were 
produced primarily by initial deposition (Nelson and Nance, 1980). 

Based on drill-hole data we have extended the area of transitional roof 
within part of Franklin County (fig. 5) using the 25-foot thickness 
line as the break point between thick Energy Shale and the area of 
rapidly varying thickness. A corridor of this roof type separates two 
lobes of thick Energy Shale and appears to extend to, or very near to 
the Walshville channel. The north-facing slope of the southern lobe is 
much steeper than the opposite slope of the northern lobe, suggesting 
that erosion has accentuated the slope. The erosion may have been 
caused by temporary diversion of the south-flowing river waters toward 
the east-southeast, forming the corridor. The genesis of the transi- 
tional roof on the east side of figure 5 is uncertain because no active 
mines exist there. 



GEOLOGIC CHARACTERISTICS OF OLD BEN NO. 24 MINE AREA 
Setting 

The mine is situated beneath the bottomlands of a small river. The 
Pennsylvanian bedrock over the longwall panels is covered by 50 to 
60 feet of Pleistocene material, which is largely composed of silts and 
clays deposited on a lake bottom. 

The longwall demonstration panels, located in mapped area A (fig. 6), 
are about 620 feet below the surface, with bedrock representing 565 feet 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 




-25— Thickness (ft) of the Energy Shale Member 

Energy Shale slightly over 25 ft (point not honored by 25 ft thickness line) 
W£$ Transitional roof (Energy Shale thickness from ft to < 30 ft) 

■ Coal-ball sites 

X Entrance shafts 



Figure 5 

Distribution and thickness of the Energy Shale Member in a portion of Franklin County, IL. Areas of transitional 
roof and all known coal-ball sites are also plotted. Townships and ranges are indicated along the map border. 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



33 




OLD BEN NO. 24 



Y/, 



g 



# 



a. 



14 



R2E R3E 



35 

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36 I 31 



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N 



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Mapped on reconnaissance 



X, Mapped in detail 



5? Entrance shafts 



Figure 6_ 



Index to mapped areas in the Old Ben Coal Company Mine No. 24. (Numbers on the map are section numbers, 
defining 1 square mile areas.) 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



of that distance. The overburden consists of about 5 percent limestone, 
80 percent shale, claystone, and siltstone, 1.3 percent coal, 3.5 per- 
cent sandstone, and 10 percent Pleistocene cover. 



Roof 

The immediate roof of the longwall demonstration panels is the transi- 
tional type described in the preceding section; about 65 percent of the 
roof is Energy Shale (fig. 7 ). The Energy Shale is a fine-grained, 
medium-gray shale that is usually poorly bedded and has some thin iron- 
stone bands and ironstone nodules roughly an inch in diameter scattered 
throughout. The gray shale rests conformably on the coal; in many areas 
the top of the coal and the bottom of the Energy Shale interfinger 
slightly. Clay mineral analysis of samples of Energy Shale from the 
longwall panel area show that it is homogeneous both laterally and 
vertically (fig. 11a). The contact between the top of the gray Energy 
Shale and the black Anna Shale is unconformable, dipping 10° to 14°. 
The angle decreases as the top of the Energy Shale is approached (fig. 8). 
This unconformity is the result of erosion that removed the gray shale 
and exposed the top of the coal seam, forming long sinuous areas from 
which gray shale is absent (fig. 9). 

Two different facies of the Energy Shale are found as immediate roof; a 
lower, carbonaceous shale facies of limited distribution, and an upper, 
widespread, light- to medium-gray shale facies. The carbonaceous facies 
ranges from medium- to dark-gray in color, is rarely more than 0.4 feet 
thick and locally contains a lycopod-dominated compression flora. This 
carbonaceous facies is generally similar to the dark-gray unit described 
from a nearby mine (Edwards et al . , 1979). The light- to medium-gray 
facies locally reaches over a hundred feet in thickness, but only rarely 
contains recognizable plant material. This facies is sometimes silty, 
varies from finely laminated to weakly laminated and often contains 
sideritic bands or bands of small pyritic nodules near the base. 

The next younger unit, the Anna Shale, overlies the eroded top of the 
Energy Shale, or the coal where the Energy Shale is absent. The bedding 
of the Anna Shale parallels the surface on which it was deposited. The 
lower part of the Anna Shale is black, very carbonaceous, fissile, hard, 
and typically has a prominent set of joints that strike about N 80° E 
with occasional minor joint sets perpendicular to it. Large disc-shaped 
concretions up to 3 feet across occur in this lower portion of the unit. 
It grades upward into a massive, very dark-gray claystone. The Anna 
Shale reaches a maximum thickness of about 4 feet but locally thins to 
zero near the central axes of sinuous areas lacking Energy Shale (fig. 10) 
Clay mineral analysis of the Anna Shale shows that the characteristic 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 




^^ Brereton Limestone 

] Black Anna Shale 

] Gray Energy Shale 

<£?•) Coal -ball areas 

— Shale -filled rolls 

\ Normal fault, downthrown side indicated 



100 ft 



Figure 7 

Plan view of roof geology at the longwall demonstration site in mapped area A. 



10 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



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INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 





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ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 




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INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



upper and lower portions differ slightly (fig. lib). Field exposures and 
preliminary chemical analyses suggest that the lower portion of the Anna 
Shale is missing locally due to nondeposition. In some small areas no 
Anna was deposited and Brereton Limestone, the next higher unit, became 
the immediate roof of the coal. The Brereton Limestone overlies the 
Anna Shale and the coal where the Anna Shale thins to zero. It is a 
gray, argillaceous, fossil iferous, fine-grained limestone, ranging in 
thickness from about 4 to 6 feet. 



Coal 

The Herri n (No. 6) Coal in the demonstration area is of high volatile B 
bituminous rank. Based on six face-channel samples from this mine, the 
coal averages 7.8 percent moisture, 36.2 percent volatile matter, 46.2 
percent fixed carbon, 9.9 percent ash, 2.6 percent total sulfur, and 
about 11,900 Btu/lb on an as-received basis. The seam dips at only 
17 feet per mile to the northeast. The cleat in the coal is poorly 
developed with a face cleat that strikes N 35° W, while the butt cleat 
varies between N 35° E and N 58° E. Both cleat surfaces have some 
localized calcite coatings. 

The coal seam ranges from 7.2 to 8.7 feet thick. Measurements of the 
coal seam thickness show a bimodal distribution (fig. 12) with two popu- 
lations corresponding to the two major roof types. The thicker coal 
occurs under the gray shale roof whereas the thinner coal is under the 
black shale roof. On the average, coal below the black shale roof is 
nearly three-fourths foot thinner, with the thinnest part located near 
the center of the channel -like black shale roof exposures. 

The thinning of the coal is related to the erosional cutout of the Energy 
Shale (fig. 8). This was confirmed by petrographic study of a series of 
full -seam columns traversing the linear Anna Shale/Brereton Limestone 
roof exposure in study area A (fig. 9). Johnson (1979), in a detailed 
petrographic study, recognized four distinct petrographic units within 
the seam along a 1,000-foot traverse (fig. 13). Significantly, the 
petrographic units are continuous except where the top unit is truncated 
or missing under Anna Shale roof. This loss of coal is attributed to 
erosion, and/or degradation due to oxidation of the peat (Johnson, 1979). 



Floor 

The floor immediately below the coal seam consists of an underclay vary- 
ing in thickness from 1 to 3 feet. The underclay usually contains many 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



Figure 11a 

Clay mineral compositions of 
the Energy Shale and roll material 



• Energy Shale 
O Roll material 




Kaohnite and chlor ite 



Expandable clay minerals 



Figure 11b 

Clay mineral analyses of the Anna Shale 
showing differences of clay mineral 
content between the upper and lower 
portions of the unit. 



Base of Anna Shale unit 
Top of Anna Shale unit 




Expandable clay minerals 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 




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ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



y^ "Energy Shale 



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Figure 13 

Correlation of macropetrographic units within the Herrin (No. 6) Coal along a 1,000-foot traverse. The units 
are I, B.B. (blue band), II, IIIA, IIIB, and IV. Vertical exaggeration within the seam is 68:1. (Modified from 
P. R. Johnson, 1979.) 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 




Kaolinite and chlorite 



Expandable clay minerals 



Figure 14 

Clay mineral composition of underclay samples. 



slickensided surfaces near the contact with the coal seam. The variation 
in the clay mineral composition of the top of the underclay throughout 
the longwall demonstration area is shown in figure 14. The underclay 
generally overlies a nodular underclay limestone, which is composed of 
small 1- to 2-inch diameter nodules of limestone in a claystone matrix. 
The nodular form of limestone may grade downward into a massive limestone. 
The thickness of the limestone ranges from 3 to 12 feet. No relationship 
was found between the variations in thickness of these floor units and 
the thickness and distribution of the roof shales. 



Rolls 

A "roll" is a general term for any linear protrusion of shale or other 
clastic material into the top of the coal seam. We interpret most rolls 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



at this mine to be erosional channels in the peat which were subsequently 
filled with clastic materials. These rolls are usually 10 to 20 feet 
wide and 1 to 4 feet thick. They have many shapes; many are broad and 
shallow with only a weakly defined low point, while others are lens- 
shaped or V-shaped in cross section. 

Despite some local erosion of the roll -fill materials, many rolls can be 
followed as far as exposures permit, and several rolls appear to be con- 
tinuous for more than 1,000 feet. The rolls tend to parallel the edge of 
Energy Shale roof areas; they may occur in subparallel pairs, or more 
rarely in triples (fig. 10). Similar features have been noted by 
Williamson (1967) who found that elongate rolls tend to be developed in 
parallel swarms or riggs in the British coal fields. Williamson attrib- 
uted the development of these features to erosion produced by a fairly 
constant current direction. Rabitz (1979) found similar features in the 
Ruhr district. 

Erosional rolls are produced in two different environments and are filled 
with two distinct materials in varying combinations. The majority of 
the rolls were developed as a part of the initial erosion of the Energy 
Shale. The initial fill material is a medium-gray shale with inter- 
laminated fine coal stringers. Its appearance and clay mineralogy 
(fig. 11a) are similar to those of the Energy Shale. 

A small number of erosional rolls were developed by tidal action after 
the erosion of the Energy Shale. These tidal channels are filled with a 
more carbonaceous, fossiliferous shale grading locally to an argillaceous 
limestone. This fossiliferous material commonly contains small coal 
fragments and stringers, marine gastropods, and other size-sorted shells 
(Harold Rollins, University of Pittsburgh, personal communication, 1981). 
During this same period, many rolls that had been developed during the 
initial erosion were selectively reused in whole, or in part, as tidal 
channels. 

The result is a variety of roll -fill materials as illustrated in figure 
15: 15a represents the initial condition of many rolls, 15b the most 
typical roll with a sharp contact between fill materials, 15c the less 
common gradational contacts between materials, and 15d the fossiliferous 
tidal material only. When the material is calcite-cemented, the plant 
fragments may be permineralized. Coal balls (with a normal peat matrix) 
have also been found in rolls at several sites and are believed to have 
been eroded from the peat in which they were formed. 

The shale body of the rolls usually contains many small normal faults, 
apparently produced through compaction of sediments while still in a 
soft state. The compaction produces normal faulting and indicates over- 
all extension in the horizontal direction. The roll-fill materials often 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



Black Anna Shale roof 




Black Anna Shale roof 




Grades into Black Anna Shale roof 




Figure 15 

Idealized cross sections of rolls showing variation in fill materials. Horizontal scale varies from <5 feet to 
>60 feet. 



20 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



slake and tend to fall out around roof bolts after mining. These falls 
usually end within the overlying Anna Shale and are fairly shallow. 



Coal balls 

Coal balls are masses of peat that have been permineral ized in place 
during or soon after peat deposition. Carbonate minerals were introduced 
into the tissues of the peat before the peat deposit was coalified, thus 
preserving the original plant materials. Identification of the plant mate- 
rials in the coal balls by T. L. Phillips of the University of Illinois 
(table 1) shows the typical peat composition for the Herri n (No. 6) Coal 
with strong dominance of lycopod trees (Phillips et al., 1977; Phillips, 1979) 

Coal balls are locally a serious obstacle to mining. While we now have a 
short-range ability to successfully predict these deposits, general pre- 
diction of coal-ball locations must await a more thorough understanding 
of their origin. 

A fresh, broken surface of these coal balls has a light brown color which 
darkens only slightly with oxidation. Size and shape of coal balls vary 
considerably. In general, coal balls are less than 1 inch to more than 
3 feet wide and are often elongated horizontally. Smaller coal balls 
(fist-sized and smaller) are usually spherical or slightly ellipsoidal in 
shape. Medium-sized coal balls (up to 1.5 ft long) typically have height- 
width ratios from 1:3 to 1:6. Where coal ball material exceeds 60 to 
70 percent of the seam, the coal balls have varied shapes and range from 
1 to 4 feet thick. 

Clarification of the spatial distribution of the coal balls was accom- 
plished by mapping coal balls both on pillar ribs and in the roof. When 

Table 1. Identified plant material by plant group 

from coal ball vertical section 3 in Area L 
(T. L. Phillips, personal communication) 



Lycopods 76.8 

Ferns (primarily tree ferns) 12.6 

Pteridosperms 7.6 

Sphenopsids 2.9 

Cordaites .1 



100.0 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 21 



coal balls were encountered, special attention was paid to both their 
association with roof lithology and their density of occurrence. Coal 
balls occurred individually, in clusters, and in concentrated groups 
defined as "coal -ball areas," ranging from about 20 feet to more than 
150 feet across. The distinction between a cluster and a coal -ball area 
was made both on the size of the accumulation and the concentration of 
coal balls. In the absence of a natural boundary, coal balls more than 
5 feet apart were considered to be outside of a coal -ball area. The large 
coal-ball areas with a dense accumulation of coal balls often show an 
increase in both size and number of coal balls toward a central point 
(fig. 16), where a core of highly concentrated coal balls may exist 
(fig. 17). At one point in area L (fig. 18), only 0.25 feet of coal 
remained in a 10-foot vertical section of coal balls. 

There is a strong association between the areas of black shale/limestone 
roof and the distribution of coal balls (figs. 18 and 10). Coal-ball 
areas B, H, I, and N partially span the boundary between Anna Shale and 
Energy Shale roof. 

A stratigraphic approach to coal -ball distribution shows two distinct 
patterns in the longwall demonstration area. Coal balls near the top of 
the seam are by far more widespread than those in lower positions in the 
seam. The mid- and low-seam coal balls are almost exclusively found 
within coal-ball areas. Where these two patterns of distribution coin- 
cide, it is not yet clear whether they are independent distribution or 
are simply preferred areas of permineralization. 

The origins of these coal balls are not fully resolved. Stratigraphic 
evidence based on the close association of coal balls with black shale/ 
limestone roof suggests that mineralization began after the initial ero- 
sion of the Energy Shale. Mineralization was also probably complete when 
coal balls with a normal peat matrix were redeposited within the fossil- 
iferous gray shale found in rolls. Preliminary carbon isotope data from 
these coal balls (T. F. Anderson, University of Illinois, personal com- 
munication, 1981) suggest the dominance of freshwater carbonates in their 
formation. The study of other coal-ball sites in the Herrin (No. 6) Coal 
should help resolve some of the questions raised at Old Ben No. 24. 
Within Franklin County there are several other coal-ball sites following 
the pattern of coal balls under the black Anna Shale roof (fig. 7). These 
sites are known only from Illinois State Geological Survey mine notes and 
cannot be mapped or sampled to check their similarity to conditions at 
Old Ben No. 24. 

The thickness of the coal seam in the coal-ball areas is greatly increased 
because the permineralization preserved the volume of the peat from later 
compaction. Therefore, coal balls provide evidence on the original 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



**%m+ ■ i 




Figure 16. Concentrated coal balls near the center of coal -ball area L. Strings form a box 0.5 meters on a side. 



'. Edge of coal -ball area 



Dense coal balls 




mm 



100 ft 



\=n 



Figure 17_ 

Map of area M showing limits of the "core" of concentrated coal balls, and a minor alteration of mine plan due to 
concentrated coal balls. 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



23 




Coal- ball 
Coal -ball area 



Energy Shale roof 
1 Anna Shale/Brereton Limestone roof 



Figure 18 

Coal balls, coal -ball areas, and roof lithologies identified during mapping of the 3 longwall panels. 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



thickness of peat at the time of mineralization. Peat-to-coal compac- 
tion ratios were derived by comparing the thickness of coal next to 
individual coal balls with the corresponding thickness of permineralized 
peat in the coal ball (Teichmiiller, 1955; Zaritsky, 1975). The coal 
balls of Old Ben No. 24 Mine show an average value of 5:1, which is 
similar to values found by Zaritsky for coal balls of similar age in the 
Donets Basin (USSR). Another set of measurements between stratigraphic 
markers in the seam gave a value of about 2.0:1 (fig. 19a). The coal 
immediately above and below each coal ball often shows extra compaction, 
and some slippage of coal (shown by slickensides) has also occurred 
(fig. 19b); these factors produce the lower compaction ratios in 
measured sections through multiple coal balls. 



MINING PROBLEMS 

Prediction of coal balls 

Problems with concentrations of coal balls occurred early in the develop- 
ment of the first longwall panel. In mining these areas, the continuous 
miners had to repeatedly receive new cutting bits due to excessive wear. 
The belt entry east of the first panel had to be offset to the east at 
coal-ball area B (fig. 18); and a smaller problem with coal-ball area F 
was encountered low in the seam on the west side of the first panel. As 
the first longwall panel was being mined, two large areas of coal -ball 
concentrations were encountered, areas D and E. The longwall shearer 
suffered damage as well as excessive wear, and advanced at the low rate 
of only 155 feet during 105 eight-hour shifts— 1.5 feet per shift com- 
pared to a normal 10 feet per shift. Explosives had to be used to break 
up the masses of coal balls in the core of each area. 

When mine development reached the west side of the second panel, coal- 
ball area L (fig. 18) was encountered. Because of these coal balls, this 
panel was shortened by 80 feet (fig. 7). Similar obstacles in area Q 
also required the third panel to be shortened by nearly 300 feet (fig. 7) 
Subsequently, the second and third panels had no serious mining problems 
due to coal balls, but because of their occurrence, approximately 
50,000 tons of coal were lost within the two panels. 

Initial mapping showed that the coal balls were closely associated with 
black shale/limestone roof, and this predictive link between coal balls 
and roof type has proven reliable. Because of the many areas of black 
shale/limestone roof in the mine, the distinctiveness of the exposure 
crossing the longwall panels was not initially apparent. With the dis- 
covery in late 1979 of another area of concentrated coal balls more than 
a mile east of the longwall area associated with the same roof exposure 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 




Figure 19 

a. Five of the 13 positions where coal and coal balls were measured separately. Lower stratigraphic marker is 
the "blue band," which is indicated by the arrows. Measured positions are at .5 m intervals. 

b. Small compaction fault under round coal ball has displaced thin coal ball about 1 cm. (Bar scale is 1 cm.) 



26 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



(fig. 10), general prediction of coal- ball occurrences can now be made 
with some assurance. In general, concentrated coal-ball areas are 
associated with a continuous sublinear area of Anna Shale/Brereton Lime- 
stone roof trending N 60° W. 



Roof stability 

The variable conditions encountered at the face were a good test of the 
longwall mining procedure. The face advanced through a number of geolog- 
ically difficult areas: (1) a massive 130-foot diameter coal -ball 
deposit; (2) one of the largest rolls documented in Old Ben No. 24 Mine, 
which was 600 feet long and cut to a maximum of 4 feet into the coal; 
(3) an unstable, slipped, and fractured roof area 2 to 3 feet high 
covering an area about 150 by 50 feet over a large roll in the first 
panel; and (4) a fault zone which ran the entire length of the second 
panel (perpendicular to the advancing face) with vertical displacement 
as great as 7.5 feet. Nowhere was roof stability serious enough to stop 
the advance of the longwall face. 

Roof control at the longwall face is good, especially if the shield 
supports are promptly advanced as soon as a cut is made by the shearer. 
The stability of the face can be a problem when faults, low angle slips, 
or roof lithology boundaries parallel the face. Several areas of slips 
associated with roof lithology boundaries paralleled the longwall face. 
During cutting of the coal at these areas, pieces of roof would fall 
before the shields could be advanced. After advance of the shields many 
small pieces would fall from the gaps in front of and between the shields 
near the face. Neither amount was great enough to hinder any operation 
of the longwall. Only the roof area just in front of the shields in the 
tailgate entry posed a continuing problem. Here pieces of the roof shale 
would pile up on the floor and have to be removed in order to advance the 
shield and pan assembly. A possible solution to this problem would be 
to bolt wire mesh to the roof to retain the small pieces. 

The greatest roof-control problem for the longwall operation exists in 
the support entries (for men, materials, ventilation, and belts). In the 
Anna Shale, minor problems in entry ways are associated with rolls, coal 
balls, and roof concretions. The top surface of a roll body of shale is 
often slickensided and may also have a thin layer of coal between the 
body of the roll and the roof shale. In both cases a plane of weakness 
is created from which the body of the roll can pull away from the roof. 
Coal balls in top coal left as roof as well as concretions in the Anna 
Shale are hazards due to slickensides that have developed around these 
concretions, allowing them to fall. 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



Within the Energy Shale, thin stringers of coal commonly extend from the 
top of the coal into the shale and form planes of weakness in the roof. 
Slips and slickensided surfaces associated with the steeply dipping trun- 
cated upper surface of the Energy Shale often cause serious problems in 
roof control . 

The contact between the top of the gray Energy Shale and the overlying 
black Anna Shale is sharp and occasionally slickensided, particularly 
where the contact dips (fig. 20). Also, slips in the Energy Shale are 
common within 150 to 200 feet from the boundary of the black shale roof; 
generally they parallel the gray shale/black shale boundary (fig. 21). 
Intersections with such slips become particularly vulnerable to failure 
(fig. 22). Two factors possibly contributing to the falls in figures 20 
and 22 include (1) the belt entry that was cut wider than the rest of the 
entries, and (2) that they were within 150 feet of the north-south fault 
system in the second longwall panel. 

The north-south fault system in the second longwall panel (fig. 7) with a 
range in vertical throw from 3.0 to 7.5 feet was only a minor problem for 
the longwall process. The face was graded across the fault, and only small 
parts of the roof fell out from the footwall side of the fault. This fault 
system had some large horizontal east-west compressive stresses in the 
downthrown block, which locally produced bad roof conditions (fig. 23) and 
slowed development of the entries for the second longwall panel. These 
entries parallel the fault system. The closest entry, only 30 feet west of 
the fault system, had the most roof-control problems with large blocks 
falling out during entry development (fig. 23). In one short section, con- 
centrated horizontal stress was relieved in the form of sizable mine bumps. 
The roof in the area of the bumps had a vertical, thin, crushed zone of 
roof shale produced by failure of the shale in east-west compression. 
Other mines in the area have also experienced roof problems caused by east- 
west compression. One mine in the general area has experimented with cut- 
ting slots in the roof of some north-south entries. The slots have been 
observed to close halfway in about a week. Additional data from hydro- 
fracting in the Mississippian strata below the Pennsylvanian shows that 
southern Illinois is under horizontal compression in an east-west direc- 
tion (Lindner and Halpern, 1978; Zoback and Zoback, 1980). 

For mapped area B shown in figure 10, the number of fallen intersections 
has been tabulated as a function of lithology and the presence of struc- 
tures that may influence falls of the immediate roof (table 2). Only roof 
falls where more than one foot of rock had come down were included. 
Tables 2 and 3 show that mine entries with an Energy Shale roof have roof- 
control problems. This same study area displays the north-south roof fall 
problem (fig. 24) associated with other mines in the region; similar roof- 
control problems in the region have been documented over the past 60 years 
in the Illinois State Geological Survey mine notes. 



28 ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 




Figure 20. 

Plan view (above) and cross section of roof fall in relation to mine and geologic setting. 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 




30 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 




Figure 22. 

Roof fall in relation to mine plan and geologic setting (plan view above and cross section below). 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



31 




Figure 23. 

North-south fractured zone in roof caused by large horizontal compressive forces. 



32 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 






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INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



Table 2. Occurrence of fallen intersections for mapped area B 
by categories of roof lithology and structure 



Energy Sh. roof Anna Sh./Brereton Ls. roof 

Falls e _,. Falls Total 
no. of 



Sample 
size No. 



Sample 



size No. % samples 



Intersections 
with slips* 



Total 

intersections 



15 



Intersections 
without slips* 293 41 



308 



47 


6 








21 


14 


191 
197 








484 
505 



* Slips are small faults, most of which are of nontectonic origin. 



Table 3. Number of mapped falls by location for mapped area B 

No. 



Falls at 
intersections 



41 



85 



Falls in entries 
between intersections 

Total falls 



7 
48 



15 

100 



Subsidence 

Subsidence of the surface over the first two longwall panels was period- 
ically monitored by Old Ben Coal Company personnel. Conroy (1978), 
Curth and Cavinder (1977), and Wade and Conroy (1977) assumed a uniform 
mined-out void height of 7 feet to calculate the percentage of surface 
subsidence/mining height over the panels. However, the actual mined-out 
void heights measured during many traverses of the operating second 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



longwall face vary between 7.2 and 8.25 feet. This introduces a 3 to 
17 percent error in calculating the ratio of subsidence/mining height if 
a 7-foot mining height is used. Even though the coal thickness ranges 
from 7.2 to 8.6 feet, the variability in mined-out void heights can also 
be related to the roof rock being brought down by the longwall mining 
operation. The average mined-out void height in the area (not affected 
by the end constraints of the panel) is about 7.5 feet. These void 
measurements were made on the gob side of the face conveyor pan from the 
floor to the roof exposed between the shields. Using the maximum sur- 
face subsidence of 5.2 feet over the second longwall panel and dividing 
it by the 7.7-foot mining height found below the monument gives a ratio 
of .67 instead of .74 when using 7 feet as the mining height. 

Figure 25a represents the subsidence profile from the second longwall 
panel and the mined-out void height measurements below the profile. It 
shows that the profile is controlled by small variations in the mining 
height. In figure 25b, the subsidence profile for the first longwall 
panel shows that the greater amount of subsidence has taken place over 
the area with thicker coal in the panel. Maximum surface subsidence over 
the first panel was 4.72 feet, and over the second panel, 5.21 feet (sur- 
vey, December 4, 1978). It was found that the second panel had a 13 per- 
cent increase in maximum surface subsidence as compared to the first 
panel. The comparison was made when the faces had advanced equally from 
the surface monuments, which show the maximum subsidence of each panel. 

This difference may be attributable to the presence of a fault system 
that runs along the length of the second panel. Large differential move- 
ments can take place along faults (Lee, 1966) and may allow larger blocks 
of rock to cave, reducing bulking. The amount of subsidence usually 
increases when a longwall panel is mined next to another longwall panel, 
as compared to the smaller amount of subsidence produced over a single 
longwall panel in a virgin coal mining area. 



Physical strength test results 

The cores for these tes 

drilling from the mine icvei. m luiai ui au icei, ui cure wab rauveiKu 

and tested for its physical strength. Testing procedures, the raw data 
and core descriptions are in appendixes A and B. 



The cores for these tests were obtained from the roof of the mine by 
drilling from the mine level. A total of 50 feet of core was recovered 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 




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ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



FURTHER RESEARCH DIRECTIONS 

Following the completion of the first three longwall panels, a decision 
was made to focus further research in three areas of interest. Our new 
objectives are 

1. to develop a fuller understanding of the depositional 
environments of the Herri n (No. 6) Coal and its roof 
units; 

2. to develop a model for permineralization of coal balls 
for prediction of their occurrence before mining; 

3. to verify the presence and nature of transitional roof 
in other nearby mines. 

The first two objectives are being pursued through stratigraphic, geo- 
chemical, and petrographic analysis, while the third objective is being 
approached through in-mine mapping. 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 37 



REFERENCES 

Chandra, R., 1970, Slake-durability test for rocks: University of London, 
Imperial College Master's thesis, Rock Mechanics Research Report, 55 p. 

Commission on Standardization of Laboratory and Field Tests of the Inter- 
national Society for Rock Mechanics, 1979, Suggested methods for 
determination of swelling and slake-durability index properties: 
International Journal of Rock Mechanics and Mining Science, v. 16, 
no. 2, p. 154-156. 

Conroy, P. J., 1978, Subsidence above a longwall panel in the Illinois 
(No. 6) Coal: American Society of Civil Engineers Annual Meeting 
Preprint, Pittsburgh, PA. 

Curth, E. A., and M. D. Cavinder, 1977, Longwall mining the Herrin (No. 6) 
coal bed in southern Illinois, in Proceedings of Third Symposium on 
Underground Mining: NCA/BCR Coal Conference, Louisville, KY. 

Deere, D. V., and R. P. Miller, 1966, Engineering classification and 
index properties for intact rock: Air Force Weapons Laboratory 
Technical Report AFWL-TR-65-116, New Mexico. 

DeMaris, P. J., and R. A. Bauer, 1978, Geology of a longwall mining demon- 
stration at Old Ben No. 24: Roof lithologies and coal balls: Illi- 
nois Mining Institute Proceedings, 1977 Annual Meeting, p. 80-91: 
Illinois State Geological Survey Reprint 1978-J. 

Edwards, W. E., R. L. Langenheim, Jr., W. J. Nelson, and C. T. Ledvina, 
1979, Lithologic patterns in the Energy Shale Member and the origin 
of "rolls" in the Herrin (No. 6) Coal Member, Pennsylvanian, in the 
Orient No. 6 Mine, Jefferson County, Illinois: Journal of Sedimen- 
tary Petrology, v. 2., no. 3, p. 1005-1014. 

Franklin, J. A., 1970, Classification of rock according to its mechanical 
properties: University of London, Imperial College Ph.D. thesis, 
Rock Mechanics Research Report T-l, 155 p. 

Harrell , M. V., 1974, Longwalling at Freeman Coal Mining Company in Illi- 
nois: Illinois Mining Institute Proceedings, 1973 Annual Meeting, 
p. 24-27. 

Johnson, D. 0., 1972, Stratigraphic analysis of the interval between the 
Herrin (No. 6) Coal and the Piasa Limestone in southwestern Illinois: 
University of Illinois Ph.D. dissertation, Urbana-Champaign. 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



Johnson, P. R. , 1979, Petrology and environments of deposition of the 
Herrin (No. 6) Coal Member, Carbondale Formation, at the Old Ben 
Coal Company Mine No. 24, Franklin County, Illinois: University of 
Illinois Master's thesis, Urbana-Champaign. 

Krausse, H.-F., H. H. Damberger, W. J. Nelson, S. R. Hunt, C. T. Ledvina, 
C. G. Treworgy, and W. A. White, 1979a, Roof strata of the Herrin 
(No. 6) Coal Member in mines of Illinois: Their geology and stabil- 
ity—Summary report: Illinois State Geological Survey Mineral Notes 
72, p. 7 (54 p.). 

Krausse, H.-F., H. H. Damberger, W. J. Nelson, S. R. Hunt, C. T. Ledvina, 
C. G. Treworgy, and W. A. White, 1979b, Engineering study of struc- 
tural geologic features of the Herrin (No. 6) Coal and associated 
rock in Illinois. Vol. 2— Detailed report: U.S. Bureau of Mines 
Contract no. H0242017, Final report, p. 2-3 (205 p.): NTIS 
call no. PB80-219462. 

Lee, A. J., 1966, The effect of faulting on mine subsidence: The Mining 
Engineer, London, v. 125, no. 71, p. 735-745. 

Lindner, E. N., and J. A. Halpern, 1978, In situ stress in North America 
—A compilation: International Journal of Rock Mechanics, v. 15, 
p. 183-203. 

Moroni, E. T., 1974, Longwall experiences in the Herrin (No. 6) Coal 

Seam: Illinois Mining Institute Proceedings, 1973 Annual Meeting, 
p. 28-34. 

Nelson, W. J., and R. B. Nance, 1981, Geological mapping of roof condi- 
tions: Crown II Mine, Macoupin County, Illinois: Society of Mining 
Engineers of AIME Paper 80-308, 1980: Illinois State Geological 
Survey Reprint 1981-A. 

Phillips, T. L., 1979, Reproduction of heterosporous arborescent lycopods 
in the Mississippian-Pennsylvanian of Euramerica: Review of Paleo- 
botany and Palynology, v. 27, p. 239-289. 

Phillips, T. L., A. B. Kunz, and D. J. Mickish, 1977, Paleobotany of per- 
mineralized peat (coal balls) from the Herrin (No. 6) Coal Member of 
the Illinois Basin, in P. H. Given and A. D. Cohen [eds.], Inter- 
disciplinary Studies of Peat and Coal Origins: Geological Society 
of America Microform Publication 7, p. 18-49. 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



Rabitz, A., 1979, Channel -shaped rock intercalations in seams of Carbon- 
iferous coal measures in the Ruhr District: Ninth International 
Congress of Carboniferous Stratigraphy and Geology, May 1979, Urbana- 
Champaign, Abstracts of Papers, p. 169-170. 

Teichmliller, R., 1955, Sedimentation und Setzung im Ruhrkarbon: Neues 
Jahrbuch fUr Geologie und Palaontologie Mh. 4., p. 145-168. 

Treworgy, C. G., and R. J. Jacobson, in press, Paleoenvironments and dis- 
tribution of Pennsylvanian age low-sulfur coal in Illinois: Ninth 
International Congress of Carboniferous Stratigraphy and Geology, 
May 1979, Urbana-Champaign, Compte Rendu. 

Wade, L. V., and P. J. Conroy, 1977, Rock Mechanics study of a longwall 
panel: Society of Mining Engineers Fall Meeting, St. Louis, MO, 
Preprint 77-1-391, 61 p. 

Williamson, I. A., 1967, Coal Mining Geology: Oxford University Press, 
London, 266 p. 

Zaritsky, P. V., 1975, On thickness decrease of parent substance of coal: 
Seventh International Congress of Carboniferous Stratigraphy and 
Geology, Compte Rendu, v. 4, p. 393-397. 

Zoback, M. L., and M. Zoback, 1980, State of stress in the conterminous 
United States: Journal of Geophysical Research, v. 85, no. Bll, 
p. 6113-6156. 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



APPENDIX A. TESTING PROCEDURES 

Unconfined strength and elastic modulus 

Immediately prior to testing, a section of core is removed from the 
plastic tubing and wrapped in tape to hold the specimen together and to 
protect it from the oil and kerosine used during sample preparation. 
Samples are cut to a right cyclinder with a saw, and the ends are lapped 
to obtain a length-to-width ratio of about 2.5 with a tolerance for non- 
parallelism of <0.0025 inch. The 2.5:1 ratio is not always maintained 
especially within a section of core where data are needed, so a short 
specimen is used. The compressive strength values of the short samples 
are in the raw state and are not normalized to any specific length-to- 
width ratios. Loading is under constant strain conditions at rates 
indicated on the raw data sheets. No caps of any type were used. 

The modulus is obtained as a tangent modulus at 50 percent of the uncon- 
fined compressive strength. The ultimate compressive strength is found 
by dividing the ultimate axial force by the area of core perpendicular 
to its axis. 



Indirect tensile strength 

Discs with thicknesses one-half the diameter of the core are used in the 
indirect tensile testing. The discs are compressed diametrically 
between high modulus platens (steel). 

The values of indirect tensile strength, a. , are calculated by the 
following equation (F = axial load, D = diameter of the disc, t = thick- 
ness of the disc): 

2F 

a t " TT Dt 



Water content 

Samples are unwrapped, prepared, and tested the same day to minimize 
moisture loss. Portions of the tested samples are used for water-content 
determinations. Moisture content is calculated as a percentage of the 
dry weight of the sample. The water content of the tested samples is 
displayed in Appendix B. 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



Specific gravity 

The specific gravity of all samples is determined by a procedure in 
accordance with ASTM D- 1188-71. The samples are oven dried and coated 
with a plastic spray, and their specific gravity is obtained from the 
comparison of their submerged weight in water to their weight in air. 



Shore hardness 

A model D scleroscope, manufactured by Shore Instrument and Manufacturing 
Company, Jamaica, New York, was used for hardness determination on com- 
pression-strength specimens. Each of the values in the summary tables is 
an average of 20 individual readings taken on the lapped end of the com- 
pressive-strength test sample at natural moisture. 



Slake durability 

The slake-durability apparatus and testing procedure was developed at 
Imperial College by Franklin (1970) and Chandra (1970). A testing proce- 
dure was later suggested by the Commission on Standardization of Labora- 
tory and Field Tests of the International Society for Rock Mechanics (1979) 

The test is intended to assess the resistance offered by a rock sample to 
weakening and disintegration when subjected to changes in water content 
due to a standard drying and wetting cycle and slight abrasion by tumbling. 

The only deviation from this procedure performed by the Illinois State 
Geological Survey Rock Mechanics Laboratory is that the samples used are 
discs or half discs of the core. Many of the shale samples are so friable 
that spheres cannot be constructed from them. Also, minimum handling of 
the samples insures that their natural characteristics are being tested. 
All samples are run in distilled water. 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



APPENDIX B. CORE DESCRIPTIONS AND TEST RESULTS 
ISGS Drill Hole LW-1 



Top of Hole 



Thick- 
ness 
(ft) 



Shale (Lawson, Carbondale Formation Member) — 
Fine grained, medium gray, noncalcareous 
with occasional hard, dark, iron bands. 
Sharp contact to 8.25 



Elevation 

Top Bottom 

(ft) (ft) 



199.33 -207.58 



Limestone (Conant) — 

Gray fossil iferous with argillaceous 
matrix. Increasing shale and carbona- 
ceous material downward. Grades into 

Shale (part of Jamestown) — 

Dark gray, limy shale, with limestone 
nodules. Lighter colored upwards. 
Grades into 



1.41 -207.58 -208.90 



1.33 -208.98 -210.32 



Coal (Jamestown) — 

Hard, very bony, with some thin vi train 
bands. Interlayered with dark-gray to 
black carbonaceous shale. Sharp con- 
tact to 



210.32 -210.82 



Shale- 
Gray, hard, calcareous, with small fossil 
fragments. Sharp contact to 



.16 -210.82 -210. 



Shale- 



Dark gray, carbonaceous, top part 
reworked; slickensided with horizontal 
calcite-filled cracks in top 1 ft. Grades 
downward into gray shale with laminae of 
fossil shells and shell fragments. Some 
shells 1 in. across. Grades into .... 5.83 



■210.98 -216.81 



INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



„- . , Elevation 

ness Top Bottom 

(ft) (ft) (ft) 

Limestone (Brereton) — 

Gray, fine grained, argillaceous, dark- 
ening downward. More argillaceous down- 
ward. The entire length shows high angle 
80° joints or fractures with calcite 
filling, 3 or 4 subparallel h to 1 in. 
apart. Grades quickly into 4.58 -216.81 -221.39 

Shale (Anna) — 

Black, hard, fissile, fine silt lenses 

at top. Several 45° slickensided planes 

and vertical joints with calcite filling . 2.91 -221.39 -224.3 

Next 2 units, not eoved— 

Gray shale roll and coal; cut out by 
entry in which we drilled. 

Shale- 
Medium gray, hard, smooth. Sharp contact. 1.2 -224.3 -225.5 

Coal (Herri n) — 

Normally bright banded, blocky, prominent 

cleat with some calcite filling. Sharp 

contact to 7.5 -225.5 -233.0 

CI ays tone- 
Dark gray, weak, slickensided, getting 
progressively calcareous towards bottom 
of core. Top not calcareous 2.16 -233.0 -235.16 

Bottom of Hole 

Total core: 24.97 ft 

Location: 974 ft north on the 21st North Entry of the 
1-11 West North Mains. 

Date: Cored from within the mine on February 2-3, 1977. 
Elevation of the base of the coal is an estimate. 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



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INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



APPENDIX B-continued 

ISGS Drill Hole LW-2 Ft above 

coal seam 
Thick- 
ness Top Bottom 

Top of Hole (ft) (ft) (ft) 

Limestone (Brereton Member) — 

Gray, fine-grained, argillaceous. 

Dark argillaceous bands near base. 

Grades quickly into 5 11.71 11.21 

Shale (Anna Shale Member) — 

Black, fissile, bedded. High angle frac- 
ture (joints) in lower foot of unit. 
Bedding inclined 14°, paralleling the 
contact with the Energy Shale. 1 cm 
thick calcite-apatite band 7 in. up from 
the base of the unit. Sharp inclined 
(14°) contact to 3.67 11.21 7.54 

Shale (Energy Shale Member) — 

Medium gray, fine grained, hard, siderite 

bands and nodules throughout. No slips 

of joints noted 7.54 7.54 

Bottom of Hole 

Location: 24th North Entry (at 1540 ft north), off the 
West North Mains (1-11 group). 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 





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INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24 



47 



APPENDIX B-continued 

ISGS Drill Hole LW-3 Ft above 

ooal seam 



Thiak- 



ness Top Bottom 

Top of Hole (ft) (ft) (ft) 

Limestone- 
Coring stopped in limestone. 

Shale- 
Dark gray, fine grained, scattered bands 
of white fossil fragments. Best fits 
description of shale unit below Conant 
limestone. Grades quickly into 83 22.8 21.98 

Limestone (Brereton? Member) — 

Medium gray, fine grained, massive. 

Grades quickly into 46 21.98 21.52 

Shale (Anna Shale Member) — 

Black, lower foot is fissile, jointed. 
Upper part massive. Beds inclined 5°. 
High angle fractures (joints) present in 
lower 2 ft. Concretion from 4.75 to 
11.5 in. above base of unit. Sharp con- 
tact to 3.06 21.52 18.46 

Shale (Energy Shale Member) — 

Medium gray, fine grained, siderite bands 
and nodules throughout. One slip encoun- 
tered in core 15.5 ft above base of unit. 
Top 2 feet of core is darker gray 18.46 18.46 0.0 

Bottom of Hole 

Location: 1442 ft north on the 24th North Entry off the West North 
Mains (1-11 group). 



ILLINOIS STATE GEOLOGICAL SURVEY CONTRACT REPORT 1982-2 



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INVESTIGATION OF ROOF AND FLOOR STRATA: OLD BEN MINE NO. 24